Kodi: I've generally noticed that placing as many trees as possible in a small space makes the map look better; however, you've essentially arranged your trees in lines, and it does not look so hot. It's not terrible with the two types of trees, but you really need to take care with where and how you place them so it doesn't look like a tree army. You've also got a pretty serious mapping error on the left. The house isn't bad, but.... windows much?
Miles: Lighten up your screen a bit. Even for being a dense, rainy jungle (well...it's rainy, anyway), it's too hard on one's eyes. Now about that dense jungle part: 1) While palm trees may grow in the jungle, they do not look good all spread out like this. 2)Jungles are dense - pack in your trees. Close is key. 3) Don't just randomly scatter multi-colored flotsam and jetsam around. It really doesn't look that great. Another suggestion would be to use some of the marsh tiles for the ground - most especially the dead leaves autotile, but also the marshy ground. If you're going for a jungle, the key is that not a lot of sun gets in, so not a lot of grass grows (this is true in forests as well), and stuff tends to collect and almost stagnate. Your map is also very square - not bad if that's the overall style of your game, but it looks rather odd by itself.